1. Field of the Invention
The present invention relates to a method for purifying an electronic item material or its intermediate product, such as a charge-transporting material for an electrophotographic photoconductor used in an electrophotographic system type copying machine, printer, facsimile or the like.
2. Discussion of Background
A material used as a charge-transporting material is required to be a material having a high purity in order to provide stable performances from an initial stage to a long period use when it is used for an electrophotographic photoconductor.
Generally, in order to provide these performances, it is essential to purify a produced crude product. As a purification method by an adsorbent, JP-A-60-233156 discloses a method comprising a combination of activated clay and activated carbon, and JP-A-4-310962 discloses a purification method comprising purifying with activated clay and then purifying with active silica. They are a method comprising a combination of several kinds of adsorbents, but JP-A-7-56365 discloses a method comprising repeating a purification treatment operation at least 2 times to improve a purification effect. These methods raise a problem of increasing a starting material cost by using many kinds of adsorbents and a problem of increasing a cost by repeating the same treatment operation. Also, a material having satisfactory electric properties required for an electrophotographic photoconductor could be sometimes obtained by treatment with an adsorbent such as activated carbon, activated clay or the like, but in many cases, a material having a satisfactory level of properties could not be obtained. On the other hand, a purification method by sublimation to obtain a high purity product achieved only a low yield, and raised industrially unfavorable problems.